Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $31.69   7.176%   $33.9641   $33.96   $33.95   $34.00  
  Purchase #2 $149.71   3.136%   $154.4049   $154.40   $154.40   $154.40  
  Purchase #3 $106.60   12.257%   $119.666   $119.67   $119.65   $119.70  
  Purchase #4 $55.46   5.842%   $58.7   $58.70   $58.70   $58.70  
  Purchase #5 $208.40   6.513%   $221.9731   $221.97   $221.95   $222.00  
  Purchase #6 $178.88   6.702%   $190.8685   $190.87   $190.85   $190.90  
  Purchase #7 $133.36   6.311%   $141.7763   $141.78   $141.80   $141.80  
  7 purchase totals = $864.10       $921.3529   $921.35   $921.30   $921.50